1. Field of the Invention
The present invention relates to a mobile communication system, and it is suitable for use in transmitting data from different sectors or wireless zones to one mobile station.
2. Description of the Related Arts
Diversity transmission in a 3GPP system (e.g. diversity transmission between sectors or between wireless zones) is realized by selection/combination and duplication/distribution between UE and RNC. In other words, identical data is transmitted and received in two or more radio transmission channels, and the transmission channels with better quality (the ones that transmit data containing fewer errors) are selected.
FIG. 1 is an explanatory diagram of a diversity transmission (DHO: Diversity Hand-Over) between base stations.
To explain the downlink, a base station controller RNC duplicates data when transmitting the data to a mobile terminal that is in a soft hand-over state and transmits the data to each base station (Node-B). Each of the base stations performs error correction encoding processing such as convolutional encoding (turbo encoding) of the received data, reduces data volume by performing puncture processing, and transmits the same transmission data to a mobile terminal UE. The mobile terminal UE combines the data received via each base station (in the example of FIG. 1, three radio transmission channels) and decodes the data.
FIG. 2 is a diagram showing a state of data volume suppression that has been caused by a puncture.
Using convolutional encoding with an encoding rate of ½, the data volume increases twice as much; however, the data volume can be suppressed by the puncturing.
Data consisting of the 9 bits X0-X8 at first becomes, for example, data consisting of the 18 bits A0-A8 and B0-B8 via convolutional encoding. Via the puncturing of the data, bits of A2, A5, A8, B1, B4, and B7 are removed as shown in FIG. 2. The data to be transmitted is consequently data consisting of 12 bits. Therefore, data consisting of 18 bits becomes data consisting of 12 bits via the puncturing, and the data volume can be reduced to ¾. The mobile terminal at the receiving end receiving the data consisting of 12 bits inserts a dummy bit into a portion of the bits removed by the puncturing, performs error correction decoding (e.g. viterbi decoding, turbo decoding) afterwards, and decodes data consisting of Y0-Y8. It is obvious that the bits Y0-Y8, if there is no bit error, have to be the same bits as X0-X8.
However, although transmission of identical data via different radio transmission channels is significant in terms of obtaining diversity gain, it is not necessarily preferable when performing intense error correction encoding/decoding processing. In fact, in the H-ARQ method, different data with different rate matching patterns is transmitted rather than transmitting the same data at the time of data retransmission.
Patent Document 1 discloses a system applying different encoding methods in accordance with transmission quality. Patent Document 1: Kohyo (National Publication of Translated Version) No. 2002-503918